Predation risk influences feeding rates but competition structures space use for a common Pacific parrotfish.

In terrestrial systems it is well known that the spatial patterns of grazing by herbivores can influence the structure of primary producer communities. On coral reefs, the consequences of varied space use by herbivores on benthic community structure are not well understood, nor are the relative influences of bottom-up (resource abundance and quality), horizontal (competition), and top-down (predation risk) factors in affecting spatial foraging behaviors of mobile herbivorous fishes. In the current study we quantified space use and feeding rates of the parrotfish, Chlorurus spilurus, across a strong gradient of food resources and predator and competitor abundance across two islands with drastically different fisheries management schemes. We found evidence that while feeding rates of this species are affected by direct interference competition and chronic predation risk, space use appears to be primarily related to exploitative competition with the surrounding herbivore community. We found no evidence that predation risk influences diurnal foraging space use in this small bodied parrotfish species. Additionally, we found the influence of chronic predation risk on feeding rates of this species to be less dramatic than the results of recent studies that used model predators to measure acute behavioral responses of other species of herbivorous fishes. Our results indicate that the non-consumptive effects of predators on the foraging behaviors of coral reef herbivores may be less dramatic than previously thought.

Currents connecting communities: nearshore community similarity and ocean circulation.

Understanding the mechanisms that create spatial heterogeneity in species distributions is fundamental to ecology. For nearshore marine systems, most species have a pelagic larval stage where dispersal is strongly influenced by patterns of ocean circulation. Concomitantly, nearshore habitats and the local environment are also influenced by ocean circulation. Because of the shared dependence on the seascape, distinguishing the relative importance of the local environment from regional patterns of dispersal for community structure remains a challenge. Here, we quantify the "oceanographic distance" and "oceanographic asymmetry" between nearshore sites using ocean circulation modeling results. These novel metrics quantify spatial separation based on realistic patterns of ocean circulation, and we explore their explanatory power for intertidal and subtidal community similarity in the Southern California Bight. We find that these metrics show significant correspondence with patterns of community similarity and that their combined explanatory power exceeds that of the thermal structure of the domain. Our approach identifies the unique influence of ocean circulation on community structure and provides evidence for oceanographically mediated dispersal limitation in nearshore marine communities.

Species-specific thermal classification schemes can improve climate related marine resource decisions.

Global climate change increasingly contributes to large changes in ecosystem structure. Timely management of rapidly changing marine ecosystems must be matched with methods to rapidly quantify and assess climate driven impacts to ecological communities. Here we create a species-specific, classification system for fish thermal affinities, using three quantifiable datasets and expert opinion. Multiple sources of information limit potential data bias and avoid misclassification. Using a temperate kelp forest fish community in California, USA as a test case for this new methodology, we found the majority of species had high classification agreement across all four data sources (n = 78) but also a number of low agreement species (2 sources disagree from the others, n = 47). For species with low agreement, use of just one dataset to classify species, as is commonly done, would lead to high risk of misclassification. Differences in species classification between individual datasets and our composite classification were apparent. Applying different thermal classifications, lead to different conclusions when quantifying 'warm' and 'cool' species density responses to a marine heatwave. Managers can use this classification approach as a tool to generate accurate, timely and simple information for resource management.

Marine protected areas do not prevent marine heatwave-induced fish community structure changes in a temperate transition zone.

Acute climate events like marine heatwaves have the potential to temporarily or permanently alter community structure with effects on biodiversity and ecosystem services. We aimed to quantify the magnitude and consistency of climate driven community shifts inside and outside Marine Protected Areas before and after a marine heatwave using a kelp forest fish community dataset in southern California, USA. Abundance, biomass, diversity and recruitment of warm-water affinity species during the marine heatwave were significantly greater compared with prior years yet cool-water affinity species did not show commensurate declines. Fish communities inside MPAs were not buffered from these community shifts. This result is likely because the particular species most responsible for the community response to environmental drivers, were not fisheries targets. Resource managers working to preserve biodiversity in a changing climate will need to consider additional management tools and strategies in combination with protected areas to mitigate the effect of warming on marine communities.

Multi-scale recruitment patterns and effects on local population size of a temperate reef fish.

Recruitment of the temperate reef fish Coris julis was studied across the Azores Archipelago (central North Atlantic), over four consecutive recruitment seasons and at three spatial scales: between islands (separated by 100s of km), sites within islands (separated by 10s of km) and transects within sites (separated by 10s of m). At the largest scale (i.e. between islands) spatial recruitment patterns were highly variable, suggesting the influence of stochastic processes. Recruitment was spatially consistent within islands, even though magnitude was unpredictable between years, indicating that processes at meso-scales are probably more deterministic. Recruits settled randomly at the transect scale, probably reflecting habitat homogeneity. It was proposed that large and island-scale patterns reflect larval availability, driven by physical and biological processes occurring in the plankton. No evidence was found for a density-dependent relationship between newly settled and 2 week settled C. julis nor between cumulative recruitment and young-of-the-year. It appears that adult density is limited by larval supply (pre-settlement regulation) at low recruitment sites, and determined by post-settlement, density-dependent processes at high recruitment sites. This work is one of few to investigate multiple spatial and temporal scales of recruitment for a coastal fish species inhabiting isolated, temperate oceanic islands and hence, provides a novel comparison to the many studies of recruitment on coral reefs and other, more connected systems.

Distribution, size frequency, and sex ratios of blacktip reef sharks Carcharhinus melanopterus at Palmyra Atoll: a predator-dominated ecosystem.

Blacktip reef sharks Carcharhinus melanopterus were the most abundant predator in the lagoons at Palmyra Atoll. They were evenly distributed throughout the lagoons, although there was some evidence of sexual segregation. Males reach sexual maturity between 940-1,020 mm L(T). Bird remains were found in some C. melanopterus stomachs. C. melanopterus at Palmyra appear to be smaller than those at other locations.